Drawing and ironing process

ABSTRACT

Prior to the drawing and ironing of a sheet or blank of a material such as untinned low carbon cold rolled steel to form a tubular article such as a can body, the metal sheet is roughened in such manner as to provide an overall, uniformly dense pattern of minute depressions in its surface. Oil or other lubricant is applied to the roughened surface and is retained within these small depressions during the drawing and ironing operation, whereby to reduce the mechanical and frictional forces on the blank and on the drawing and ironing dies and thus eliminate galling of the dies and minimize fracture of the metal.

[451 June 20, 1972 [54] DRAWING AND IRONING PROCESS [72] Inventors:Richard Robert Bolt, Lake Villa; Delbert Edmond Wobbe, Cary, both ofI11.

[73] Assignee: American Can Company, New York, N.Y.

[22] Filed: Jan. 27, 1969 [21] Appl. No.: 794,141

[52] US. I .72/41, 72/349 [51] Int. Cl. ..B2ld 22/28, B2ld 37/18 [58]FieldotSearch ..72/4l,42, 43,39, 40,53,

[56] References Cited UNITED STATES PATENTS FOREIGN PATENTS ORAPPLICATIONS 621,535 4/ 1949 Great Britain 406,891 8/1944 Italy .Q..72/43 625,01 1 6/ l 949 Great Britain ..72/ 349 PrimaryExaminer-Charles W. Lanham Assistant Examiner-E. M. CombsAttorney-Kenneth I-l. Murray Robert P. Auber, Leonard R. Kohan, GeorgeP. Ziehmer and Frank .1. Jordan ABSTRACT Prior to the drawing andironing of a sheet or blank of a material such as untinned low carboncold rolled steel to form a tubular article such as a can body, themetal sheet is roughened in such manner as to provide an overall,uniformly dense pattern of minute depressions in its surface. Oil orother lubricant is applied to the roughened surface and is retainedwithin these small depressions during the drawing and ironing operation,whereby to reduce the mechanical and frictional forces on the blank andon the drawing and ironing dies and thus eliminate galling of the diesand minimize fracture of the metal.

3 Claims, 3 Drawing Figures DRAWING AND IRONING PROCESS BACKGROUND ANDEXPLANATION OF THE. INVENTION One of the most successful processespresently being utilized for forming deep, seamless container bodiesfrom flat blanks is known as the drawing and ironing process andinvolves first drawing the blank into shallow cup form in one or moredrawing operations and thereafter thinning and elongating the sidewallsof the cup in one or more ironing operations.

The drawing dies usually produce a relatively shallow cup having bottomand sidewall thicknesses substantially equal to the original thicknessof the blank. Thereafter, the ironing dies thin the sidewall of thedrawn cup and cause retrograde flow of the metal, thereby increasing theheight of the cup while leaving the thickness of its bottomsubstantially unchanged. If desired, a drawing or redrawing die may bedesigned to also function as an ironing die, as for example disclosed inour U.S. Pat. No. 3,203,218, granted on Aug. 3, 1965.

As used herein, the term drawing means the forming of recessed parts byforcing the plastic flow of metal in dies, and refers to the operationwherein a peripheral margin of a flat blank is turned inwardly andsimultaneously smoothed by means of a drawing punch and die to form acup having a wrinkle free sidewall whose thickness is substantiallyequal to the thickness of the original blank, while ironing means athinning of the sidewall of a drawn cup by forcing the cup through toolswherein clearance between punch and die is less than the thickness ofthe sidewall. In an ironing operation, the sidewall of the cup iselongated by reducing its thickness with no reduction in the insidediameter of the cup. It is generally accomplished by placing the cup ona closely fitting punch and forcing the cup and punch through anironing,or reducing,die whose diameter is slightly less than the outerdiameter of the cup, thereby forcing the excess metal back and producinga longer but thinner sidewall. This ironing operation imposes severefrictional stresses on the metal of the cup, and if proper lubricationof the ironing die is not effected, some of the metal of the cup isdeposited on the die. This metal build-up, or galling, sooner or latterresults in the tearing or fracture of the cups as they are forcedthrough the die.

While the drawing and ironing process has been used extensively in themanufacture of seamless containers from blanks having surfaces whichhave a self-lubricating property, such as made of aluminum, or steelelectrocoated with a softer ductile material such as tin as disclosed inour U.S. Pat. No. 3,360,157, granted Dec. 26, 1967, difficulty has beenencountered in utilizing this technique in the manufacture of seamlesscontainers from steel blanks having no ductile metallic coating. This isthought to be due principally to the fact that uncoated steel surfaceserves little or no lubricating function, as the blank is forced throughthe ironing dies, and the lubricant which is applied to the blank iswiped off by the upper edge of the ironing die and thus does notproperly lubricate the die face or the blank during the ironingoperation. Since the ironing process subjects such blanks to extrememechanical deformation and friction, galling of the ironing die and theconsequent fracture of the blank results.

It has been found that this can be minimized, or substantiallyeliminated, if the surface of the steel blank is roughened in suchmanner as to form small shallow pockets which function as smallreservoirs to hold the lubricant which is applied to the blank prior to,and sometimes during, the drawing and ironing operations. Thesereservoirs, while reduced in size,

remain in existence throughout the drawing operations and 1 While theprinciples of this invention may provide benefits when used with othertypes of metal stock, it is primarily useful when used with steel stockwhich is not provided with a surface coating or a more ductile metalsuch as tin. For the purpose of this invention, such steel stock will bereferred to as uncoated stock or black plate, and includes various typesof stock known in the trade as T.F.S. (tin free steel), some of which dobear extremely thin flash coatings of chromium or chromium compoundswhich do not have the ability to function as or become impregnated witha lubricant.

The preferred manner of effecting this roughening is by sand blastingthe metal stock with a fine gritty material. such as sand or aluminumoxide in such manner as to obtain a uniform, dense pattern of smalldepressions. These depressions are gradually reduced in depth, or ironedout, during the formation of the container body, but it is desirablethat they be of sufficient depth so that they are not completelyeliminated until the need of lubrication no longer exists. Thus, as ageneral rule, the depressions should remain in existence, in graduallyshallowing form, during all ironing operations,

although it is desirable for purposes of appearance of the finished bodythat they be finally eliminated in the final ironing operation. However,it is necessary that they be of sufficient depth,as they enter thisfinal ironing operation, to hold sufficient lubricant to prevent gallingof the final ironing die.

The sand blasting of the metal stock is preferably effected on the sheetor web from which the body blanks are cut, prior to the blankingoperation, since there is a tendency for warpage to occur if theindividual blanks are sand blasted. In addition, both sides of the stockare preferably sand blasted in order to minimize warpage.

While the primary need for lubricant is on the outside surface of theside wall of the cup in order to prevent galling of the ironing dies, ithas been found that the roughening of the inner surface of this sidewallis very desirable to reduce friction between the cup and the punch, andthus facilitate stripping of the drawn and ironed cup from the punch.Despite this, the roughening of only the outer surface of the blank isstill a substantial advance in the art, since in some instances theroughening of the interior is not necessary.-

It will be understood that while the benefits of the invention areapplicable to the drawing operation they are not essential to it,whereas they are absolutely essential to the ironing operations. Thus,it would be possible to first draw the shallow cup from unroughenedstock in a conventional drawing operation and then sand blast andlubricate either one or both surfaces of the walls of the cup prior tothe ironing operations, which would be effected in a press separate fromthe drawing press. However, present commercial practice makes it mostfeasible to roughen the flat blank prior to both the drawing and ironingoperations.

While sand blasting, which term for the purposes of this invention isused to describe a process wherein any suitably gritty particulatematerial, which may or may not be sand, is projected against the blankto roughen its surface, is the preferred method of roughening the blank,the invention is notso limited, and other methods, such as acid etching,mechanical abrasion by means of rolls or brushes, etc., may be utilized.

An object is to provide a practical method of drawing and ironing athin-walled, cup-shaped steel container from uncoated steel stock. I

A further object is to provide a method of drawing and ironing anuncoated steel blank without galling of the dies or fracture of thestock.

A still further object is to provide a method of forming a drawn andironed container from uncoated steel wherein adequate lubrication duringthe ironing steps may be readily and easily accomplished.

Numerous other objects and advantages of the invention will be apparentas it is better understood from the description, which, taken inconnection with the accompanying drawing discloses a preferredembodiment thereof.

In drawing and ironing an article from a flat blank made from a materialsuch as uncoated low-carbon sheet steel, the steel is treated byblasting its surface with a gritty material such as aluminum oxide orsand to provide a uniformly roughened surface containing a high densityof minute depressions. The pre-roughened blank is then placed in adrawing and ironing press where a punch forces it through a drawing dieto form it into a shallow, seamless cup. Thereafter, the sidewall of thedrawn cup is forced through one or more ironing dies which thin andelongate the sidewall. Prior the drawing operation and especiallyprior'the ironing operations, the blank is coated with a lubricant, andsufficient lubricant is retained in the small depressions of theroughened surface during these forming operations to reduce themechanical and frictional forces between the blanks and the drawing andironing dies. There is thus produced a drawn and ironed one-pieceuncoated steel container having a seamless sidewall whose thickness isless than the end wall.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary perspectiveview of a marginal edge portion of a steel blank having its top andbottom surfaces roughened in accordance with the principles of theinstant in vention;

, FIG. 2 is a sectional view of a drawing and ironing apparatus which isused to form the blank of FIG. 1 into a seamless container utilizing themethod of the instant invention; and

FIG. 3 is a perspective view of a seamless container produced by theapparatus of FIG. 2.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENT As a preferred orexemplary embodiment of the instant invention, there is provided acircular blank formed of low carbon, cold rolled steel havingmetallurgical qualities which render it suitable for withstanding thestresses imposed upon it by a drawing and ironing process. An example ofa suitable type ofsteel is one having the following percentage chemicalanalysis:

Carbon 0.05-0.12 Manganese 0.25-0.60 Sulphur 0.05 maximum Phosphorous0.02 maximum Silicon 0.l0 maximum Copper 0.20 maximum Iron balanceTypical average mechanical properties of such a steel are:

Ultimate tensile strength 73,200 p.s.i. Yield strength 70,700 p.s.i.Tensile elongation 13% Impact elongation 1% Hardness 67 R 30 T Thissteel is of the type known as black plate, and may be chemically treated(either before or after the hereinafter described sand blastingtreatment) to protect it against corrosion, as by being provided with anextremely thin coating of an inorganic chemical composition, asexemplified in U. S. Pat.

No. 2,8l 3,8 l2, granted Nov. 19, 1957, or with a flash coating of ametal such as chromium, as exemplified in U. S. Pat. No. 3,113,845granted Dec. 10, 1963. Plate of the former type is known as CTS(Chemically Treated Steel), while the latter type is generally known asTFS (Tin Free Steel). Heretofore, it has not been possible to draw aniron such types of steel on a commercial basis because its surfacecondition, even when well covered with lubricating oil, has been such asto cause galling of the ironing dies.

We have discovered that this galling of the dies can be eliminated ifthe steel is treated, prior to the-drawing and ironing operations, byblasting its surface with a hard particulate material such as sand oraluminum oxide in orderto roughen them. The blasting-operation may beeffected by utilizing commercially available air blasting equipment andwill be of the metal sheet. For example, when sand blasting the low.

carbon, cold rolled steel,.it is preferable to use aluminumoxide of gritor finer, and preferably in the order of 80 to 240 grit, or sand in theorder of 50 to mesh. Other materials and particulate sizes may be used,depending on various factors such as the properties of the metal beingblasted, the characteristics of the drawing and ironing dies, the sizeand configuration of the article being formed, and the properties of thelubricant to be used during the forming process. By way of example, airblasting low carbon, cold rolled steel with 80 grit aluminum oxideproduced a 70 microinch average RMS with a 320 microinch maximum, whilea grit aluminum oxide produced a 30 microinch-average RMS with a250microinch maximum,

The surface roughened blank 10 is operated upon by the'ap-' paratus ofFIG. 2, the operation and structure of which is covered in our U. S.Pat. No. 3,203,218, granted Aug. 3], 1965. The apparatus comprises astack of dies, generally designated 14, mounted within a die holder 16.Both the die stack 14 and the die holder 16 are mounted in a suitablepress which may be hydraulically or mechanically actuated. The

topmost die 18 in the stack 14 is a combined drawing andironing dieformed with a central aperture 20 which has a rounded drawing face 22 atits upper surface and an ironing face 23 immediately therebelow.

A cylindrical forming punch 24 having a flat bottom surface 26 of anysuitable configuration is reciprocally mounted above the die 18 in axialalignment with the die aperture 20.

The fiat circular blank 10 is inserted between the die 18 and an annularblank holder 28 disposed above the die. The blank holder 28 is formedwith a central aperture 30 having an inner diameter slightly greaterthan the diameter of the punch 24. A spaced series of guide holes 32extends through the blank holder 28 adjacent its outer edge. Studs 34having shanks 36 and heads 38 are threadably engaged with the die holder16 with their shanks 36 extending upwardly through the holes 32 in theblank holder 28 to prevent the blank holder 28 from moving transverselyrelative to the die 18, while permitting it to move to some extent alongthe longitudinal axis of the die.

The lower surface of the blank holder 28 has formed in it a circularrecess 40 of substantially the same diameter as that of the blank 10 andhaving a depth which is slightly less than the thickness of the blank10, the recess 40 serving to position the blank in axial alignment withthe die aperture 20. When thus positioned, the marginal edge portion 42of the blank 10 is gripped between the die 18 and the blank holder 28with a substantial predetermined force due to the action of a pluralityof heavy compressed springs 44 which are disposed about the stud shanks36 and held between the blank holder 28 and the stud heads 38. It willbe realized that means (not shown) are provided to raise the blankholder 28 against the pressure of the springs 44 at a suitable time topermit the feeding of the blank 10 into position.

Prior to its insertion into the apparatus of FIG. 2, the blank '10 iscoated with a suitable lubricant which fills the depressions on itsroughened surfaces 12. Ordinary motor oil ranging in viscosity fromS.A.E. 20 to S.A.E. 40 has been found to be satisfactory for thepurposes of this invention, but-other lubricants may of course be used.

The upper end of the punch 24 is attached to a piston rod 46 which isactuated by a suitable power source such as hydraulic cylinder (notshown). When actuated, the punch 24 moves downwardly, bringing itslower'surface 26 into contact with the blank 10.

As the downward movement of the punch 24 is continued, the centerportion of the blank is forced downwardly into the aperture and themarginal edge portion 42 of the blank 10 is progressively forced frombeneath the blank holder 28 and into contact with the drawing face 22and ironing face 23 of the die 18 and is drawn and ironed into a tubularconfiguration to form a sidewall of a shallow cup.

During this operation, the force with which the marginal edge portion 42of the blank 10 is gripped between the blank holder 28 and the die 18 ismaintained at a level sufficient to insure that the blank 10 is notwrinkled or folded as its marginal edge portion 42 is withdrawn.

As the marginal edgeportion 42 is carried through and reshaped by thedie 18, at least some of the lubricant which is contained in thedepressions on the outside surface of the cup (the undersurface of theblank 10) functions to lubricate the die 18 and to reduce the frictionbetween it and the blank 10. This result is had because the depressionsare not ironed out by the die 18, although they are reshaped and madesomewhat shallower by it. Thus, the sidewall of the cup which is formedby the die 18, as it leaves the die 18 still has shallowlubricantcontaining pockets in its surfaces.

While its upper portion is still engaged by the die 18, the shallow cupenters a second die 48 mounted in the die holder 16 below the first die18. The second die 48 is an ironing die and has an ironing face 50 whichis smaller in diameter than and axially aligned with the ironing face 23of the die 18. A spacer plate 52 is disposed between the die 18 and thedie 48 to produce a predetermined spacing between them. The downwardmovement of the punch 24 forces the sidewall of the shallow cup past theironing face 50, thereby reducing the thickness of and also elongatingits sidewall.

During this ironing operation, the lubricant which is present in thestill-roughened surfaces of the shallow cup serves to lubricate the die48 and prevent metal build-up on it. Preferably, the characteristics ofthe roughened surfaces 12 and the dimensions of the die 48 are such thatthe small depressions are not completely removed in this ironingoperation, and carry some of the lubricant through the die 48 and thusmake it available for the next ironing operation, which is effected by athird die 54 which has an ironing face 56 and is mounted in die holder16 below the ironing die 48 and is suitably spaced therefrom by a spacer58.

The ironing face 56 is aligned with and has a diameter somewhat smallerthan that of the ironing face 50. As the punch 24 continues downwardly,it carries the cup into the ironing face 56, thus effecting a furtherironing operation on the side wall of the cup to furtherreduce itsthickness and increase its height and produce a drawn and ironedcontainer or can body 60. As stated, the walls of the cup, as they enterthis die 56, still contain remnants of the original depressions, andthese contain lubricant which serves to lubricate the die 54. Desirably,these depressions are substantially eliminated, or ironed out, by thedie 54, which is the last die in the die stack 14. This elimination ofthe depressions is desirable to improve the appearance of the finishedproduct, and is possible because there are no subsequent dies whichrequire lubrication. It will be realized that the cup, as it enters thefinal die 54 in the stack must carry enough lubricant in its surfacedepressions to lubricate this die and prevent it from galling.

While it has been indicated that the depressions may carry in them asufficient quantity of the original lubricating oil to provide adequatelubrication for the whole drawing and ironing process, it will berealized that it may be desirable to add additional lubricant to theblanks during the process. This can easily be done by drilling holes inthe die holder 16 and spacer rings 52,58 and using them to injectadditional lubricant against the outside surface of the sidewall of thecup as it is forced downwardly by the punch 24.

The drawn and ironed container body 60 (see FIGS. 2 and 3) has a bottomend 62 of substantially the same thickness as that of the blank 10 and asmooth sidewall 64 whose thickness is substantially less than that ofthe blank 10. It is to be understood that, while the drawings show threedies in the die stack 14, any suitable number of dies may be used toproduce a desired sidewall length and thickness in the body 60. In allcases, it is desirably that the cup, as it enters the final die 54,still have some shallow, lubricant containing depressions in itssurface.

After passing through the ironing die 54, the container 60 is strippedfrom the punch 24 by a conventional stripper, generally designated 66.The stripper 66 consists of a segmented flat annular ring 68 comprisinga series of segments 70 adapted to slide radially within a recess 72 inthe lower surface of the die holder 16. The segments 70 are urgedradially inwardly by springs 74' and are retained within the recess 72by an annular flat retaining ring 76 secured to the die holder 16 bybolts 78. At the extreme inwardly position of the segments 70, thesegmented ring 68 has a substantially cylindrical inner surface 80 whosediameter is slightly less than the diameter of the punch 24, with asmoothly rounded upper edge 82 anda sharp lower edge 84.

As the formed container 60 is conveyed toward the stripper by the punch24, it contacts the rounded upper edge 82 of the segmented ring 68,forcing the segments 70 outwardly to allow the punch 24 and container 60to pass through the ring 68. After the container 60 .has passed throughthe ring 68, the springs 74 move'the segments 70 inwardly against thepunch 24.

The actuating means for the punch 24 then move it upwardly. During theupward movement of the punch 24, the upper rim 86 of the formedcontainer engages the sharp lower edge 84 of the segmented ring 68. Thisprevents upward movement of the container 60, thereby stripping it fromthe punch 24. While the rim 86 of the container 60 is shown as beingsmooth and level, in practice it is usually rather uneven, and atrimming operation is required'to produce the smooth rimmedconfiguration of FIG. 3.

It is apparent from the foregoing description that the roughenedsurfaces 12 on the interior and exterior side faces of the cup aresubjected to different mechanical actions during the drawing and ironingprocess. The internal side wall surface is forced to undergo a 90tensional bend during the drawing operation and a tensional force duringironing, whereas the exterior side wall surface undergoes a 90compressive bend in the drawing and is then exposed to an extrusion or"squeezing action when passing through the ironing dies.

Because of the different mechanical actions, the exterior surface of thecup undergoes a deformation and change different from that of theinterior surface. With each ironing step, the exterior surface undergoessevere deformation as it is squeezed between the particular ironing faceand the punch and the oil-containing depressions in the surface becomeshallower. However, these depressions are not completely eliminated, atleast until the final ironing die, and retain a sufficient amount of oilso that during this squeezing the oil that has been retained within thedepressions on the surface of the blank provides lubrication for thesevere mechanical working and bumishing to which the metal is subjected.

As mentioned hereinbefore, the interior side wall is only forced toundergo a 90 tensional bending in the drawing operation, and elongatedor stretched during the ironing operation without being mechanicallyworked or burnished during ironing. Accordingly, the surface on theinterior sidewall may, if desired, be initially roughened to a somewhatlesser degree in terms of the density and depth of depressions than thesurface of the exterior sidewall. Alternatively, the roughening of thesurface on the interior side wall may be completely dispensed with.However, it is preferred that the interior sidewall have the same degreeof roughness as the outside sidewall to retain lubricating oil to reducethe sliding friction between the punch 20 and the interior sidewall ofthe container during ironing, and to facilitate the stripping operation.

- The functioning of the above described apparatus of FIG. 2 inreshaping a flat blank into a cup-shaped container body is described ingreater detail in our aforementioned U. S. Pat. No. 3,203,218. While theinstant invention has been described asapplicable to the apparatus andmethod of that patent, it will be understood that it is not limited toit, and that it may be utilized in conjunction with other drawing andironing systems. One such other system does not utilize a combineddrawing and ironing die 18 of the type shown in the die stack 14, butinstead, as an initial step, forms a shallow cup from the flat blank ina separate cupping press by a drawing operation, and then transfers thecup to an ironing press where a redrawing operation and several ironingoperations are carried out.

The roughening of the blank surface as herein described is generally notnecessary in a straight drawing operation where the thickness of thesidewall is not substantially reduced, but it is necessary in an ironingoperation where galling of the dies, and consequent tearing of the metalof the blank, or of succeeding blanks, occurs if it is not done. Thus,the principles of the instant invention are generally applicable to anymetal reforming operation wherein an ironing operation is utilized. Itis thought that the invention and many of its attendant advantages willbe understood from the foregoing description and it will be apparentthat various changes may be made in the form, construction, andarrangement of the parts and in the steps of the method described andtheir order of accomplishmentwithout departing from the spirit and scopeof the invention or sacrificing all of its material advantages, the formbeing hereinbefore described being merely a preferred embodiment.

We claim:

1. In the method of forming a seamless container body having a sidewallwith a smoothouter surface and a bottom wall of a substantially greaterthickness than the sidewall from a thin flat blank by progressivelybending concentric annular planar segments of said blank into acylindrical sidewall to form a cup shaped article in a drawing operationand by thinning and elongating the sidewall of said cup-shaped articlein more than one ironing operation to form said seamless container body,the improvement which comprises:

providing an uncoated low carbon steel blank; forming shallowdepressions in at least one surface of said uncoated low carbon steelblank, which will form the outer surface of said cup-shaped article,prior to the drawing operation by sand blasting said one surface withfinely divided particulate material, selected from the group consistingof aluminum oxide having a particle size within the range of to 240 gritand sand having a particle size within the range of 50 to mesh, which vproduces a roughness on said one surface within the range ofapproximately 70 microinch average RMS with a 320 microinch maximum to30 microinch average RMS with a 250 microinch maximum; applying alubricant to said one surface of said uncoated low carbon steel blankprior to the drawing operation for entrapping lubricant in saiddepressions; and

maintaining said depressions at a reduced depth in said outer surface ofsaid cup-shaped article while passing said cup through at least oneironing operation.

2. In the method of forming a seamless container body according to claim1 wherein said depressions formed in said outer surface of saidcup-shaped article are eliminated in the final ironing operation.

3. in the method of forming a seamless container body according to claim1 wherein said depressions are formed in at least one surface of a webof uncoated low carbon steel, from which said flat blank is cut, by saidsand blasting step, said one surface subsequently forming the outersurface of said cupshaped article.

t i I! t

1. In the method of forming a seamless container body having a sidewallwith a smooth outer surface and a bottom wall of a substantially greaterthickness than the sidewall from a thin flat blank by progressivelybending concentric annular planar segments of said blank into acylindrical sidewall to form a cup shaped article in a drawing operationand by thinning and elongating the sidewall of said cup-shaped articlein more than one ironing operation to form said seamless container body,the improvement which comprises: providing an uncoated low carbon steelblank; forming shallow depressions in at least one surface of saiduncoated low carbon steel blank, which will form the outer surface ofsaid cup-shaped article, prior to the drawing operation by sand blastingsaid one surface with finely divided particulate material, selected fromthe group consisting of aluminum oxide having a particle size within therange of 80 to 240 grit and sand having a particle size within the rangeof 50 to 100 mesh, which produces a roughness on said one surface withinthe range of approximately 70 microinch average RMS with a 320 microinchmaximum to 30 microinch average RMS with a 250 microinch maximum;applying a lubricant to said one surface of said uncoated low carbonsteel blank prior to the drawing operation for entrapping lubricant insaid depressions; and maintaining said depressions at a reduced depth insaid outer surface of said cup-shaped article while passing said cupthrough at least one ironing operation.
 2. In the method of forming aseamless container body according to claim 1 wherein said depressionsformed in said outer surface of said cup-shaped article are eliminatedin the final ironing operation.
 3. In the method of forming a seamlesscontainer body according to claim 1 wherein said depressions are formedin at least one surface of a web of uncoated low carbon steel, fromwhich said flat blank is cut, by said sand blasting step, said onesurface subsequently forming the outer surface of said cup-shapedarticle.